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Energy Consumption and Stability Investigation
of Constant Temperature and Humidity Test Chamber
Kwesi Mensah
Graduate School of Mechanical Engineering, Hanbat National University
125 Dongseodaero Yuseong-gu Daejeon, 34158 Korea
kwesimensah7@gmail.com
Jong Min Choi
*
Department of Mechanical Engineering, Hanbat National University
125 Dongseodaero Yuseong-gu Daejeon, 34158, Korea
jmchoi@hanbat.ac.kr
Received 24 October 2016
Accepted 7 February 2017
Published 9 March 2017
Temperature and humidity chambers are used to simulate many thermal-environmental condi-
tions, as well as to observe the e®ects that a range of temperature and humidity have on a product
or material at the manufacturing stage. The energy consumption and accuracy of these test
chambers over the last decades have raised concerns for recent researchers. In this study, the
energy consumption and stability of a temperature and humidity chamber was investigated under
various operating and environmental conditions by adopting a variable speed compressor to the
refrigeration unit. The accuracy of temperature and humidity was also investigated. It is found
that, for a given surrounding environmental condition, as the dry bulb temperature conditions of
the temperature and humidity chambers increased, the cooling capacity of the system increased
while the refrigerating unit's power decreased for all operating conditions. However, the total
energy consumption of the test unit increased due to an increment in the electric heater output. In
maintaining e®ective stability of temperature and humidity test chambers, it is observed that,
varying the refrigeration unit capacity by adjusting compressor speed has the potential for
reducing the temperature and relative humidity °uctuations within the chamber for a given
operating condition. Adopting a variable speed compressor to the refrigerating unit, have the
potential for reducing the energy consumption signi¯cantly according to increment of setting
temperature of the chamber as well as ensuring system stability for temperature and
humidity chambers.
Keywords: Temperature and humidity chamber; energy consumption; electric heater; variable
speed compressor; refrigerator.
*
Corresponding author.
International Journal of Air-Conditioning and Refrigeration
Vol. 25, No. 1 (2017) 1750010 (11 pages)
©World Scienti¯c Publishing Company
DOI: 10.1142/S2010132517500109
1750010-1
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1. Introduction
Industries such as manufacturing, engineering, food
processing and packaging performs climatic-related
environmental tests with the variation of pressure,
temperature, humidity and moisture e®ects as well
as mechanical environmental tests to evaluate
product's reliability and quality at various condi-
tions before releasing product to the general market.
These tests are also necessary in ensuring product
quality and avoiding the cost and loss of reputation
that is likely to occur after a manufactured product
fails on the general market due to the performance
change and low durability in the actual environ-
mental conditions. Figure 1shows various categories
of environmental testing available and some exam-
ples of the tests being conducted. Several types of
test chambers including pressure, humidity or tem-
perature chambers for climatic chambers, and vi-
bration, thermal shock and stress chambers, are
used to measure the performance of products under
shock or vibration.
Conventional temperature and humidity cham-
ber is equipped with air circulating fans, refrigera-
tion unit, electric heater, and humidi¯er for
simulating the thermal-environmental condition.
These conventional test chambers are also equipped
with constant speed compressor adopted to the re-
frigeration unit to operate at all test conditions.
1
The temperature and humidity chamber consumes a
lot of energy during its operation. Available litera-
tures and researches have focused on the calibration
and characterization.
2–6
design for speci¯c purpose.
7
and improvement in aesthetics and controls.
8
of
environmental chambers. Pad¯eld.
9
developed an
open-top climatic chamber for simulating tempera-
ture and humidity gradients across a wall or roof.
Pad¯eld's design presented di®erent options for
performing experiments and for monitoring the test
specimen. Feng et al.
7
developed a low cost tem-
perature chamber for precision measurements.
Thermoelectric coolers were used for the cooling of
the inside chamber circulating air directly. This
eliminates the e®ects of vibration as reported in the
previous design.
10
Current innovative chambers have improved
aesthetics and easier operating interfaces allowing
researchers to test products faster. The signi¯cant
area of improvement in environmental testing
chambers has been in the control electronics. This
allows operators to observe and program the con-
dition of the test specimen with ease. In an experi-
mental investigation on the performance of
temperature and humidity chamber, Mensah et al.
11
indicated that a variation in the operating condi-
tions of these chambers will result in a correspond-
ing variation in the power consumption of the
system. Rare literature is found on the performance
of these environmental chambers in the aspect of
energy consumption with variation of operating and
environmental conditions, and on the information
about environmental test chambers. In this paper,
the basic structure and function of the environ-
mental chamber were introduced, the energy con-
sumption and performance of a temperature and
humidity chamber was investigated under various
operating and environmental conditions by adopt-
ing a variable speed compressor to the refrigeration
unit. Also the use of variable speed compressor for
minimizing test chamber °uctuations and ensuring
chamber stability is analyzed.
2. Environmental Test Chamber
An environmental chamber is an enclosure used to
test the e®ects of speci¯ed environmental conditions
on biological items, industrial products, materials,
and electronic devices and components. Its interior
chamber environment is regulated or controlled to a
speci¯c set of parameters. Such chambers can be
used: as a stand-alone test for environmental e®ects
on test specimens, or as preparation of test speci-
mens for further physical or chemical tests, or fur-
ther as environmental conditions for conducting
Environmental Tesng
Mechanical Tesng Clima c Tesng
Combined Tesng
Shock Vibrao n Fague
Example of Tests:
Temperature Pressure Humidity/
Moisture
Example of Tests:
Fig. 1. Categories of environmental testing with some
examples.
K. Mensah and J. M. Choi
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testing of specimens. Environmental chambers
range in size from small bench-top boxes to huge
computer-controlled walk-in rooms, depending on
the desired tests. Climatic tests, such as air pressure,
humidity, temperature and light, and dynamic or
mechanical tests, i.e., shock, vibration, acceleration,
rotation, etc. Climatic test chambers are used for
performing climatic tests. An example is the tem-
perature and humidity chamber. Climatic test such
as humidity and moisture e®ect on a manufactured
product helps to access at early stages, the degrad-
ing e®ect of water damage on a product. High
moisture content in a product may result in corro-
sion between conductive components of the product,
whereas an extremely low humidity may result in
brittleness. High temperature e®ects in a product
testing may promote oxidation and chemical reac-
tions, changes in resistance, inductance and capac-
itance capabilities of the test specimen, as well as
formation of metal compounds (thermal di®usion)
on the test specimen, etc. Low temperature testing
of a product may cause moisture to freeze on the
product, increase heat losses, cracking e®ects on
¯nished surfaces, etc.
1
Climatic test chambers can be distinguished with
the type of temperature range that test chamber is
operated.
12
The type of chamber cooling mechanism
has also been used to distinguish between climatic
chambers. Main reported cooling mechanism cate-
gory includes, the use of expendable refrigerants or
use of mechanically cooled refrigeration systems.
Expendable refrigerants are liquid/gases that can be
injected directly into the space being cooled or into
heat exchangers. As the liquid enters the chamber
(directly or through a ¯n coil), it absorbs heat and
°ashes into a gas. The gas is then expelled and
vented out of the chamber and it is normally passed
through ducts mounted outdoors. Common refrig-
erants used for this purposes are liquid nitrogen
(LN2Þand liquid carbon dioxide (LCO2Þ.
13
Figure 2
shows a schematic diagram for a temperature and
humidity testing chamber. Existing mechanically
cooled climatic chambers adopts a single speed
compressor to the refrigerating unit.
6,9
Not many
works have been conducted on the investigation of
energy savings potential of mechanically cooled
temperature and humidity test chambers.
11
The
next section investigates experimentally the energy
saving potential and analyzes the possibility of
minimizing chamber °uctuation of climatic chamber
under varying operating and environmental
conditions by adopting a variable speed compressor
to the refrigerating unit.
2.1. Stability of temperature and
humidity chamber
Maintaining stable conditions within a climatic test
chamber is crucial for monitoring the performance
and condition of the test specimen. Temperature
and humidity control is critical in the preservation
of manufactured products and test specimens since
unacceptable levels of these parameters generally
contribute signi¯cantly to the breakdown of pro-
ducts and materials. A rapid increase in tempera-
ture increases deterioration reaction rate and melts
heat-susceptible materials. A change in relative hu-
midity causes dimensional alteration in hygroscopic
materials (for example, wood and other organic
materials), resulting in delamination of sensitive
materials. One major challenge has been to ensure
minimum and acceptable °uctuation range of tem-
perature and humidity test chambers in performing
product testing at the manufacturing level. Mea-
sures such as use of special regulators to react with
temperature and humidity disturbances both inside
and outside the chambers as well as use of special-
ized envelopes for insulation purposes are not always
su±cient.
14
Due to the on-o® control scheme of
many electric heater and humidi¯er components,
Kazanskaya.
14
indicated that, in order to ensure a
Electric Heater
Humidif er
Evaporator
Test Chamber
Circula ting Fans
Ret urn Ai r
Refrigeration unit
Supply Air
Compres sor
Heat
Exc ha ng er
Exp ansi on
Device
Fig. 2. Schematic diagram of a climatic chamber.
Energy Consumption and Stability Investigation of Constant Temperature and Humidity Test Chamber
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minimum temperature °uctuation for a constant
temperature chamber, the frequency of periodic
temperature °uctuations at the electric heater inlet
should not exceed the system locking frequency for a
given °uctuations amplitude. The IEC60068.
2,3
and
ISO 17025.
15
provides a series of calibration meth-
ods and guidelines for environmental test chambers
in the aspect of ensuring an acceptable °uctuation
ranges for various types of environmental testing
chambers. Rare literature is found with regards to
experimental investigations.
This study investigated experimentally the po-
tential of ensuring stable setting conditions within a
400 L capacity temperature and humidity chamber
with the adoption of a variable speed compressor
technology to the refrigerating unit.
2.2. Operating principle of temperature
and humidity chamber
Generally, climatic chambers such as temperature
and humidity chambers are designed to control and
maintain temperature and relative humidity at set
points within the working chamber (space), as de-
termined by the operator at the front control panel
of the system. The working chamber refers to the
volume of space where the product to be tested is
placed. As shown in Fig. 2, air is constantly circu-
lated through the chamber by using the circulating
fans. The circulating air passes through the evapo-
rator of the refrigerator, electrical heater, and hu-
midi¯er in series. Cooling and dehumidi¯cation are
achieved by using the evaporator of the refrigeration
system. The temperature is regulated by adjusting
the electric heater's output. The humidity is set up
by adding water vapor to the chamber circulating
air by humidi¯er.
3. Experimental Setup and Test
Procedure
Figure 3shows the schematic diagram for the ex-
perimental setup. The test unit is placed in a con-
trolled environment (surrounding) equipped with an
electric heater, humidi¯er and a refrigerating unit to
ensure stable surrounding conditions for the test unit.
The surrounding controlled environment helps to
monitor e®ectively, the performance of the test unit.
The size of the test specimen working chamber
was 0.82 0.7 0.7 m
3
. The refrigeration system
was installed at the lower portion of the system
while the working chamber was located at the upper
portion of the chamber. In order to perform test at
various compressor speeds, a compressor with an
inverter control is adopted. The experimental test
was conducted according to the variation of tem-
perature and humidity. The test conditions are set
by the operator at the front control panel. The
compressor was operated at the maximum speed to
obtain low temperature and humidity condition.
Since there were no generally accepted standard
for the test procedure of a temperature and hu-
midity chamber in the aspect of power and energy
consumption of the test chamber, the experiments
were performed at varying dry bulb temperature
range from 20Cto45
C. The relative humidity
was also varied within the range of 25% to 55%. The
compressor speed was varied within 25 to 60 Hz for
the operating condition of the test chamber. The
surrounding dry bulb and wet bulb temperatures of
the temperature and humidity chamber were ¯xed
at 27C and 19C respectively to avoid the perfor-
mance change of the refrigerator. Once the system
and the surrounding reached a steady state, the
experimental data were recorded continuously for
30 min with 2-s interval, and then averaged over the
test period. Table 1shows the detailed experimental
test conditions that were conducted.
Dry bulb temperature and relative humidity
sensor were used to measure chamber inside condi-
tions with an accuracy of 0.1C and 0.5%,
respectively.
Refrigerant temperatures and pressures at the
selected locations in the experimental setup as
shown in Fig. 3were measured using thermocouples
and pressure transducers. Thermocouples were used
to monitor the temperature of air at the inlet of the
electric heater. The power input to the test system
was measured by using a power meter with an un-
certainty of 0.01% of full scale. Table 2shows the
detailed speci¯cations of the test unit.
A temperature sensor and a relative humidity
sensor at the working space of the chamber were
monitored by the controller (A TEMI 2500
16
).
When the system started to operate, the refrigerator
was turned on at the ¯xed speed. The temperature
and humidity were controlled by the heater outputs
to electric heater and humidi¯er, respectively. All
heater outputs were adjusted by using a SSR to get
a quick reply.
K. Mensah and J. M. Choi
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Table 1. Experimental test conditions.
Test unit's setting condition Test unit's surrounding condition
DB RH Compressor speed DB WB
C%Hz CC
Low temperature conditions
20 —50,60,70 27 19
15 —50,60,70
10 —50,60,70
5—50,60,70
Compressor speed variation
25 40 25,30,40,50,60,70 27 19
35 25,30,40,50,60,70
45 25,30,40,50,60,70
Relative humidity variation
15,25,35,45 25 40 27 19
15,25,35,45 35 40
15,25,35,45 45 40
15,25,35,45 55 40
Fig. 3. Schematic diagram of experimental setup.
Energy Consumption and Stability Investigation of Constant Temperature and Humidity Test Chamber
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4. Results and Discussions
To examine the energy saving potential of the
temperature and humidity chamber adopting vari-
able speed compressor to the refrigeration unit, se-
ries of experiments were conducted at varying
operating and environmental conditions. This
section discusses the various results that were ob-
served by comparing and analyzing the results of a
conventional test chamber and the proposed new
system.
4.1. Conventional temperature and
humidity chamber performance
This subsection discusses the results of a conven-
tional temperature and humidity test chamber with
a ¯xed refrigeration unit's compressor speed of 60 Hz
operated within the dry bulb temperature range
of 20C and 45C inclusive and a relative humid-
ity of 40% for dry bulb temperatures above 0C.
Constant speed compressor refrigeration systems
have been adopted in all conventional climatic test
chambers.
10,14,17
Figure 4shows the variation of power consump-
tion according to the variation of dry bulb temper-
ature. The setting dry bulb temperature is varied
from 20Cto5C. Under low temperature con-
ditions (negative temperatures), the relative hu-
midity of the test chamber is assumed to be zero.
The humidi¯er is turned o® automatically when the
relative humidity is assumed to be zero. The test
was conducted under no-load condition. No-load
condition refers to the condition where no test
specimen is placed within the temperature and hu-
midity chamber. For a ¯xed compressor speed, it is
observed that increasing the dry bulb temperature
resulted in an increase in the power consumption of
the test unit. Generally, the cooling capacity of the
vapor compression refrigeration unit increases with
an increment of evaporator inlet air temperature,
while the power consumption decreases due to a
decrease of pressure ratio of the compressor. The
total power consumption of the test chamber in-
creased even though that of the refrigeration unit
decreased. This was because increasing rate of the
electric heater output was higher than the decreas-
ing rate of refrigerator power consumption. The
electric heater output increased with an increment
of setting temperature due to an increment of the
refrigerator capacity. Figure 5also shows an incre-
ment in test unit power consumption when the
setting dry bulb temperature is varied from 25Cto
45C and at a ¯xed relative humidity of 40%.
Fig. 4. Variation of test unit power consumption with dry
bulb temperature.
Table 2. Temperature and humidity test chamber speci¯cations.
Test unit speci¯cations
Internal Size (WDHÞ0:82 0:70.7 (m)
Material External material Steel plate, surface electrostatic spraying
Internal material Stainless steel plate
Insulation materials Polyurethane foam
Refrigerator Refrigerant R-22
Compressor Inverter scroll type, rated capacity 10.7 kW
Evaporator Fin tube type, 6-rows and 7
Condenser Fin tube type, 6-rows and 20
Heater for dry bulb temperature 7.0 kW (SR control)
Heater for humidi¯er 2.0 kW(SSR control)
K. Mensah and J. M. Choi
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An increase in the dry bulb temperature results in
an increase in the condensing and evaporating
temperatures of the refrigerating unit. However, the
rate of increment in the evaporating temperature is
higher than the rate of increment in the condensing
temperature for the given operating condition as
shown by Fig. 6.
In these conventional test units, the cooling ca-
pacity of the refrigerator unit is normally selected to
cover the lowest expected temperature condition of
the temperature and humidity test chambers.
However it can be stated that, varying evaporating
temperature of refrigeration unit as a result of
varying dry bulb operating temperature, will lead to
a varying cooling capacity of the refrigerating unit.
Hence it is imperative for the cooling capacity of
temperature and humidity chambers to be adjusted
according to varying operating condition for opti-
mum performance of the system.
Figure 7shows the variation of dry bulb tem-
perature with evaporator exit temperature. It is
observed that, increasing the dry bulb temperature
also increases the evaporator exit air temperature,
while the increasing rate of dry bulb temperature of
the chamber is higher than it of the evaporator exit
air temperature. This may be because the refriger-
ator cooling capacity increased according to an in-
crement of dry bulb temperature. The evaporator,
heater and humidi¯er are arranged serially as shown
in Fig. 3. A smaller increasing rate in the evaporator
exit air temperature than it in the dry bulb tem-
perature resulted in an increase in the air tempera-
ture di®erence across the inlet and outlet of electric
heater for a ¯xed compressor speed and relative
humidity as shown in Fig. 8.
These variation in temperature di®erences can
a®ect the test unit stability for a given operating
conditions. Minimizing the temperature variation
across the electric heater and humidi¯er is very
important for e®ective monitoring of the perfor-
mance of the test specimen.
From the analysis and observations outlined in
Sec. 4.1, it is therefore highly recommended that,
20 25 30 35 40 45 50
-10
-8
-6
-4
46.0
46.5
47.0
47.5
48.0
48.5
49.0
49.5
50.0
Relative humidity = 40%RH
Compressor speed = 60Hz
Saturation Temperatures (
o
C)
Dry bulb temperature (
o
C)
Evaporating
Condensing
Fig. 6. Variation of refrigeration unit saturation temperatures
with test unit dry bulb temperature.
20 25 30 35 40 45 50
5
10
15
20
25
30
Relative humidity : 40%RH
Compressor speed = 60Hz
Evaporator Exit Air Temperature (
o
C)
Dry bulb temperature (
o
C)
Fig. 7. Evaporator exit air temperature variation with dry
bulb temperature at highest compressor speed.
20 25 30 35 40 45 50
8.0
8.4
8.8
9.2
9.6
10.0
Compressor speed = 60Hz Relative humidity : 40%RH
Power consumption (kW)
Dry bulb temperature (
o
C)
Fig. 5. Variation of test unit power consumption with dry
bulb temperature.
Energy Consumption and Stability Investigation of Constant Temperature and Humidity Test Chamber
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test unit's refrigeration capacity and the test unit
system °uctuation should be adjusted and opti-
mized according to the operating conditions to in-
crease system performance and to save energy.
Section 4.2 investigates the potential of using vari-
able speed compressor technology adopted to the
refrigeration unit to adjust the refrigeration unit
capacity according to the operating condition, and
to also minimize test unit °uctuation and improve
system stability and ¯nally to reduce the energy
consumption of conventional test units.
4.2. Variable speed compressor
temperature and humidity
chamber performance
Figure 9shows the variation of power consumption
according to the variation of compressor speed and
dry bulb temperature respectively. Under low tem-
perature conditions (negative temperatures), the
relative humidity of the test chamber is assumed to
be zero. It is observed that, for a ¯xed operating
condition of the test chamber, an increase in the
compressor speed of the refrigerating unit yields a
corresponding increase in the power consumption of
the test chamber while the same operating condition
is maintained. Also, increasing the dry bulb tem-
perature also resulted in an increase in the power
consumption of the temperature and humidity
chamber. Increasing the dry bulb setting tempera-
ture within the chamber increases the cooling
capacity of the refrigerating unit while the power
consumption of it is reduced. However, the heater
output increases with increase in dry bulb setting
temperature and hence causing the test unit's total
power consumption to increase. The refrigerators'
cooling capacity is regulated by varying the com-
pressor speed for a ¯xed operating condition.
It is seen from Fig. 9that, at 20C, it is possible
to operate the compressor at speeds 50, 60 and 70 Hz
and same setting condition is maintained. However,
at 60 Hz (simulating the conventional test cham-
bers), the power consumption is 3.77 kW while at
50 Hz, the power consumption is 3.16 kW. This
means that, operating the compressor at minimum
speed of 50 Hz, a potential for minimizing the energy
consumption of temperature and humidity test
chambers. Similar trend can be observed when
the dry bulb temperature is varied from 20C
to 5C.
Figure 10 shows the variation of power con-
sumption according to the variation of compressor
speeds for dry bulb temperatures of 25C, 35C and
45C at a ¯xed relative humidity value of 40%.
It can be seen that, at test unit operating condi-
tion of dry bulb temperature of 45C, it is possible to
vary the compressor speed between 25 and 70 Hz
inclusive, and the same test condition is maintained
within the test unit. At a compressor speed of 25 Hz,
the power consumption is 5.9 kW while at 70 Hz, a
9.66 kW of power was recorded. This means that, it
is better to operate the test unit at the minimum
compressor speed (25 Hz) to reduce the power
-25 -20 -15 -10 -5 0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
Power consumption (kW)
Dry bulb temperature (
o
C)
Compressor speed (Hz)
50Hz
60Hz (Conventional Test Unit)
70Hz
Fig. 9. Variation of power consumption according to dry bulb
temperature of the chamber and compressor speed.
20 25 30 35 40 45 50
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
Relative Humidity = 40%RH
Air Temperature Difference
across Electric Heater (
o
C)
Dry bulb temperature (
o
C)
Compressor Speed = 60Hz
Fig. 8. Air temperature variation with dry bulb temperature
across heater.
K. Mensah and J. M. Choi
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consumption than operating it at higher compressor
speeds of 60 Hz (as in the case of conventional test
unit) or 70 Hz as showed in Fig. 10.
Figure 11 shows the variation of the evaporator
exit air temperature with compressor speed. It is
observed that, as the compressor speed reduces, the
evaporator exit air temperature increases for all dry
bulb temperature conditions. An increase in the
evaporator exit air temperature for a ¯xed dry bulb
temperature and relative humidity, causes a reduc-
tion in the air temperature di®erence across
the heater. Figure 12 shows the variation of air
temperature di®erence with compressor speed
for di®erent dry bulb temperatures across the
electric heater.
Minimizing the air temperature di®erence across
the electric heater can make the heater output small
hence causing a reduction in the power consumption
of the test unit for a given operating condition.
Figures 13–15 show the temperature and hu-
midity variations within test specimen working
space for compressor speeds of 40, 30 and 25 Hz re-
spectively at the setting condition of 25C dry bulb
temperature and 40% relative humidity value. It is
observed from Figs. 13–15, reducing the compressor
speed for the given operating conditions results in a
decrease in the chamber °uctuations. This is be-
cause, reducing the compressor speed, for a ¯xed
20 25 30 35 40 45 50 55 60 65
0
4
8
12
16
20
24
28
32
36
40
Relative humidity = 40%
Evaporator Exit Air Temperature (
o
C)
Compressor Speed (Hz)
Dry bulb temperature (
o
C)
25
35
45
Fig. 11. Evaporator exit air temperature variation with com-
pressor speed.
20 25 30 35 40 45 50 55 60 65
4
5
6
7
8
9
10
11
12
13
14
Air Temperature Difference
across electric heater (
o
C)
Compressor Speed (Hz)
Dry bulb temperature (
o
C)
25
35
45
Relative humidity = 40%
Fig. 12. Air temperature variation with dry bulb temperature
across heater.
0 200 400 600 800 1000 1200 1400 1600 1800
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
Tmin
Tmax
Compressor : 40Hz
Setting condition:
25
oC and 40%RH
Temperature
Relative Humidity
Time (Sec)
Temperature (
o
C)
12
16
20
24
28
32
36
40
44
48
52
RH
min
RH
max
Relative Humidity (%)
Fig. 13. Temperature and relative humidity of the chamber at
40 Hz.
20 30 40 50 60 70 80
2.2
4.4
6.6
8.8
11.0
Power consumption (kW)
Compressor speed (Hz)
Dry bulb temperature (
o
C)
25
35
45
Relative humidity : 40%RH
Fig. 10. Variation of power consumption according to com-
pressor speed for various dry bulb temperatures.
Energy Consumption and Stability Investigation of Constant Temperature and Humidity Test Chamber
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relative humidity value, the air temperature at the
exit of the evaporator decreases as shown in Fig. 11.
This causes a reduction in the air temperature dif-
ference across the electric heater as shown in Fig. 12,
hence causing the °uctuations within the system to
reduce. It is therefore recommended that, test units
should be operated at minimum speeds in order to
increase the stability of the operating conditions.
5. Conclusion
Temperature and humidity test chambers are
used for testing of manufactured specimens in many
industrial and manufacturing industries globally.
In this study, the energy consumption and perfor-
mance of a 400 L capacity temperature and
humidity chamber has been investigated under
various operating and environmental conditions by
adopting a variable speed compressor to the refrig-
eration cycle. It was found that, a 60% reduction in
the compressor speed (from 70 to 25 Hz) results in
energy savings of about 49.2% of the total power
consumption when the dry bulb temperature is be-
tween 45C and 25C and the relative humidity is at
40%. When the dry bulb temperature is between the
ranges of 20C and 5C, a 29% reduction in the
compressor speed (from 70 to 50 Hz) results in about
28% energy savings of the total power consumption
of the test chamber. By regulating the compressor
speed, the total power of the test unit can be re-
duced at all test conditions.
In ensuring e®ective stability of temperature and
humidity test chambers, it is observed that, reduc-
ing the compressor speed by 43% (from 70 to 40 Hz)
can reduce the temperature and relative humidity
°uctuations within the chamber by 43% and 61%,
respectively, when the chamber dry bulb tempera-
ture is operated with 25C and 45C. Adopting a
variable speed compressor to the refrigerating unit
has the potential for reducing the energy consump-
tion signi¯cantly at all test conditions of the
chamber as well as ensuring system stability for
temperature and humidity chambers.
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